# cat sucks.php
<?
$loc = setlocale(LC_ALL, 'tr_TR.UTF-8');
echo $loc;
require_once "include/test.class.php";
echo User::isLoggedIn();
?>



# cat include/test.class.php
<?
class User{
        static function isLoggedIn(){
                return true;
        }
}
?>


Gives:

tr_TR.UTF-8
Fatal error: Call to undefined method User::isloggedin() in /var/www/sucks.php on line 5




System - debian with:
# locale -a
C
...
en_US.iso885915
en_US.utf8
german
POSIX
tr_TR.utf8